(1) Field of the Invention
The present invention relates to a method of and an apparatus for supplying assist air into a combustion chamber direct injecting fuel injection valve of, for example, a vehicle engine, to micronize a fuel directly injected into a combustion chamber of the engine by the fuel injection valve.
(2) Description of the Related Art
A combustion chamber direct injecting fuel injection valve according to a prior art for a vehicle engine faces a combustion chamber of the engine. A fuel injected by the fuel injection valve is mixed with and micronized by assist air and enters the combustion chamber.
According to the prior art, pressure for supplying the assist air is kept constant. When a suction valve of the combustion chamber is opened, this pressure is sufficiently larger than pressure in the combustion chamber. Namely, a large pressure difference is secured between the assist air supplying pressure and the combustion chamber pressure. As ignition timing approaches after the suction valve is closed, the pressure difference rapidly decreases and becomes nearly zero just before the fuel injection valve stops injecting the fuel.
Namely, according to the prior art, the combustion chamber pressure rises during the latter period of fuel injection of the fuel injection valve, to drop the pressure difference between the combustion chamber pressure and the assist air supply pressure, to thereby deteriorate the fuel micronization effect of the assist air and the combustion efficiency of an air-fuel mixture in the combustion chamber.